iio TJie America/i Geologist. Febmarj', i900 
been surrounded by a series of spheroidal isothermal sur- 
faces of mean temperatures. The one next the surface rep- 
resented a mean temperature of, say, boiling water at a tem- 
perature corresponding to the greater pressure of the heavier 
atmosphere existing. Above this isothermal shell were 
others representing mean temperatures of 200°, 90'', 60°, 32°, 
o**, etc. to -x'' Fahr., the extreme cold of interplanetary 
space." 
As fast as the internal heat of the earth was exhausted, 
these spheroidal isothermal shells of mean temperature 
shrunk in upon the earth and their contact with its surface 
marked the lines of corresponding climates. 
The outer, partly condensed spheroids formed transcal- 
ent layers, which tended to conserve the earth heat and shut 
out the solar heat rays, though solar light rays were more 
readih' transmitted. 
When the isothermal spheroid having a mean tempera- 
ture of 32" Fahr. shrunk in upon the earth, the oceans began 
to accumulate water at its maximum density and the Ice 
age began. The continental areas lost their resident heat 
while the oceans were still warm; so that the cold continents 
converted the vapor from the oceans into dense fogs. ''From 
the moment that snow began to accumulate, the remaining 
earth heat was available for producing those conditions 
favorable to glaciation, namely, warm seas, dense fogs, and 
cold continental areas, and the solar energy reaching the 
upper regions of the atmosphere was available for maintain- 
ing those favorable conditions. Those conditions would ob- 
tain until "by the chilling of the oceans to about 31*^ F., 
and by the glaciation of continental areas, the air was 
cleared of obscuring clouds and fogs, the uniform series of 
climates was at an end." 
A well marked rise in temperature has occurred since 
the culmination of the Ice age and is still in progress. Solar 
energy has been the only known source of heat during this 
time and by it the change in temperature is explained as 
follows: By contact with the earth's surface the direct solar 
rays are converted into dark heat rays and, as the atmos- 
phere is more transcalent to the former than to the latter, a 
part of the heat is effectual!}' trapped. 
